The possibility of feedback control of gene transcription by the protein products of gene activity in the cytoplasm will be examined by injection of an enzyme into frog egg cytoplasm in advance of the time when the enzyme is normally synthesized during embryonic development. Thus the genome will be confronted with products that it would normally synthesize later. Unlabeled enzymes will be injected into the fertilized egg, and the embryo then grown in the presence of labeled amino acids so that newly synthesized enzyme (if any) can be distinguished from injected unlabeled enzyme. Haploid parthenogenetic mouse embryos can be produced by a variety of treatments of the unfertilized egg. However, none of these haploid embryos ever developed past early stages of embryogenesis. This may be due to the absence of normal metabolic activation of the egg that occurs as the result of fertilization. Thus the embryo may be abnormal from the outset. This possible abnormality can be circumvented by fertilizing mouse eggs and then by microsurgery, removing the sperm nucleus prior to fusion of the male and female pronuclei. Such eggs do cleave and their developmental potentiality can be tested by implanting the eggs into hormonally prepared female mice.